The present invention relates to an abrasive machine, more precisely relates to an abrasive machine, which comprises a holding unit for holding a work piece, e.g., a semiconductor wafer, and an abrasive plate having an abrasive face, which abrades a surface of the work piece by relatively moving the abrasive plate with respect to the holding unit. For example, the abrasive face abrades a surface of a semiconductor wafer, in which semiconductor chips are formed, like a mirror face.
Recently, circuits in semiconductor devices are highly integrated, so flatness and surface conditions of silicon wafers, etc., which will be substrates of semiconductor devices, must be highly improved. Further, insulating layers and cables paterns, which are formed on the wafer so as to form the devices, are abraded with higher flatness. Therefore, the abrasive machine must abrade the surfaces of the wafers, like mirror faces, with higher accuracy.
In a conventional abrasive machine, a whole surface of a wafer is uniformly pressed onto an abrasive face of an abrasive plate by an airbag of a wafer holding unit.
The wafer holding unit of the conventional abrasive machine will be explained with reference to FIGS. 9 and 10.
In FIG. 9, an abrasive plate 50 is rotated about a vertical shaft. An abrasive cloth 51 is adhered on an upper face of the abrasive plate 50 so as to form an abrasive face 52. The wafer holding unit 60 is provided above the abrasive plate 50. The wafer holding unit 60 is rotated about a vertical shaft and moved in the vertical direction.
The wafer holding unit 60 includes: a head 62 having a concave section 62a, whose opening section is headed downward; a wafer holding plate 64 having a holding face, on which the wafer 12 is held; an elastic member 66, whose outer edge 66b is fixed to an enclosing section 62b of the head 62 and whose inner edge 66a is fixed to an outer end section 64a of the wafer holding plate 64, being formed like a plate and capable of allowing the wafer holding plate 64 to move within a very small range; and an air-tightly sealed chamber 65 being formed, in the head 62, by the wafer holding plate 64 and the elastic member 66.
A vacuum unit 67 for sucking and holding the wafer 12 is communicated to sucking holes 67a, which are opened in a bottom face of the wafer holding plate 64, which acts as a wafer holding face, via an air tube 67b. By actuating the vacuum unit 67, the wafer 12 can be sucked and held on the wafer holding face of the wafer holding plate 64.
A pressurizing unit 68 supplies pressurized fluid to the chamber 65 so as to press the wafer 12 onto the abrasive face 52 of the abrasive plate 50 together with the wafer holding plate 64.
A pressure reducing unit 69 reduces inner pressure of the chamber 65.
A male tapered section 70, whose outer diameter is gradually reduced downward, is downwardly projected from an inner ceiling face of the head 62; a female tapered section 72, whose inner diameter is gradually increased upward, is upwardly projected from an upper face of the wafer holding plate 64. With this structure, the male tapered section 70 fits in the female tapered section 72 when the pressure reducing unit 69 reduces the inner pressure of the chamber 65.
In the conventional abrasive machine, the surface 12a of the wafer 12 to be abraded is capable of quickly following inclination, etc. of the abrasive face 52 because of the airbag function of the elastic member 66, e.g., a rubber plate, so that the whole surface 12a of the wafer 12 can be uniformly pressed onto the abrasive face 52 even if the abrasive face 52 is inclined. With this action, the whole surface 12a can be uniformly abraded or polished like a mirror face.
By fitting the male tapered section 70 in the female tapered section 72, the wafer holding plate 64 can be precisely positioned, so that the wafer 12 can be positioned or adhered at a correct position. Therefore, abrading accuracy and abrading efficiency can be improved, and abrading steps can be executed automatically.
However, in the conventional abrasive machine, the surface 12a of the wafer 12 is pressed onto the abrasive face 52 of the abrasive cloth 51, which is adhered on the abrasive plate 50, while abrading or polishing the wafer 12. A part of the abrasive cloth 51, on which the wafer 12 is pressed, is slightly caved downward with respect to other parts, so that a concave portion 51a (see FIG. 10) is formed. And, a lower outer edge 12b of the wafer 12 contacts an inner face of the concave portion 51a and is abraded thereby.
If the lower outer edge 12b of the wafer 12 is abraded by the inner face of the concave portion 51a of the abrasive cloth 51, the abrasive face 52 is waved and badly abraded, so that flatness of the abraded surface 12a of the wafer 12 is made lower.
The abrasive face 52 of the abrasive cloth 51, which has been waved and badly abraded, can be recovered by recovering means. In the conventional abrasive machine, for example, the recovering means, e.g., a dummy wafer, a ceramic plate, is attached to the wafer holding plate 64 of the holding unit 60, then the recovering means is pressed onto the abrasive face 52 so as to recover the damaged abrasive face 52. In the case of a new abrasive cloth 51, a surface condition of the new abrasive cloth 51 is uniformed by the recovering member.
The step of recovering the abrasive cloth 51 cannot be simultaneously executed with the abrasive step. If the recovering step is executed before or after the abrasive step, required time of the abrasive step and the recovering step must be longer and working efficiency cannot be improved.
Conditions, e.g., pressing force, rotational speed of the wafer holding plate 64, in the abrasive step are different from those in the recovering step, but the wafer holding plate 64 is used in the both steps. Therefore, the rotational speed of the wafer holding plate 64 and the pressing force applied to the wafer holding plate 64 (the inner pressure of the chamber 65) must be newly set when the abrasive step or the recovering step is executed. The change of the conditions is troublesome, so that working efficiency and manufacturing efficiency cannot be improved.
An object of the present invention is to provide an abrasive machine, which is capable of preventing deformation and bad abrasion of the abrasive cloth, maintaining flatness of the abrasive face of the abrasive plate and improving abrading accuracy.
To achieve the object, the abrasive machine of the present invention comprises:
a holding unit for holding a work piece; and
an abrasive plate having an abrasive face, which abrades a surface of the work piece by relatively moving the abrasive plate with respect to the holding unit,
wherein the holding unit includes:
an inner head having a first concave section, whose opening section is headed toward the abrasive face of the abrasive plate;
an outer head having a second concave section, in which the inner head is provided and whose opening section is headed toward the abrasive face of the abrasive plate,
a holding plate being provided in the first concave section and having a holding face, on which the work piece is held;
an elastic holding member being fixed to the inner head and the holding plate, allowing the holding plate to move with respect to the inner head, and forming a first chamber for pressing the work piece in the first concave section with the holding plate;
an outer enclosing member being provided to the outer head and enclosing the inner head;
an inner enclosing member being provided between the outer enclosing member and the inner head and enclosing the inner head;
a pressing member for pressing the abrasive face of the abrasive plate, the pressing member being formed into a ring shape enclosing the holding plate;
an elastic ring member being fixed to the outer enclosing member and the inner enclosing member, holding and allowing the pressing member to move with respect to the outer head, and forming a second chamber in the second concave section; and
a pressurizing unit introducing pressurized fluid into the first chamber and the second chamber so as to press the work piece onto the abrasive face of the abrasive plate with the holding plate and so as to press the pressing member onto the abrasive face of the abrasive plate.
In the abrasive machine of the present invention, the pressurized fluid is introduced into the first chamber of the inner head, so that the work piece, which has been held by the holding plate, can be pressed onto the abrasive face of the abrasive plate. Further, the pressing member can be pressed onto the abrasive face of the abrasive plate by pressurizing the second chamber. With this action, the pressing member can be pressed onto the abrasive face of the abrasive plate while the surface of the work piece is abraded, so that flatness of the abrasive face can be maintained, and working efficiency and abrading accuracy of the abrasive machine can be improved.
In the abrasive machine, the pressurized fluid may be introduce into the first chamber by a first pressurizing unit, and the pressurized fluid may be introduce into the second chamber by a second pressurizing unit. With this structure, the pressing member can be pressed onto the abrasive face of the abrasive cloth with pressing force corresponding to pressing force for pressing the work piece onto the abrasive face. Therefore, the work piece can be abraded with higher abrading accuracy.
The abrasive machine may further comprise:
an inner head driving unit for rotating the inner head about a shaft, which is arranged perpendicular to the surface of the work piece, which has been held by said holding plate; and
an outer head driving unit for rotating the outer head about another shaft, which is arranged perpendicular to the surface of the work piece, which has been held by said holding plate. With this structure, rotaitonal speed of the work piece and the pressing member can be separately and properly controlled, so that the abrading accuracy can be improved.
In this abrasive machine, the inner enclosing member may be separable from the outer head, connected to the outer head by the elastic ring member so as to be moved together with the outer head, and rotatably held by the inner head with a bearing. With this structure, the inner head and the outer head including the inner enclosing member can be separately rotated and properly positioned.